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I was hoping I could get some opinions on a recommendation made by my contractor. The house is less than a year old and we have found many problems with the ductwork, mainly with the return being severely undersized. The contractor has fixed the returns by adding two more 30 x 8 return grilles and by running one 12 and one 10 flex duct from the new grilles back to the return box which is mounted on the side of the furnace in the attic. According to him I now have a total of 2.9 sqft of return duct area going back to the furnace. Here is my equipment information (Goodman): The furnace is model GMT090-4B, the condensing unit is a CKL42-1B (3.5 ton), and the coil is a CACF0422B2A (3.5 ton). All ductwork is flex.

My question is regarding return filter area. I currently have one 25 x 16 x 1 in the return filter box thats mounted on the side of the furnace. Thats only 400 sqin of filter area and Goodman recommends a min. of 770 sqin. Originally the contractor wanted to put another return box on the other side of the furnace with another 25 x 16 filter, but because of space limitations it would be tough. So he recommends installing a 5 pleaded filter between the side of the furnace and the current return box. According to the literature he showed me the 5 filter has more than enough filter area (78 sqft). To me the 5 filter sounds like the way to go. What to you guys think? Based on the area of return duct I now have and the proposed 5 filter would this mean all return components are sized correctly now?

Your contractor needs to do a Manual D analysis of the duct system,to determine if it's sized correctly.This requires the detals of the entire duct system,to be able to tell if it's sized correctly.

Another way they could tell is to test the supply and return ESP(external Static Pressure),to see if it's low enough to allow the addition of the PD(pressure drop) of the media filter.The ESP's when found and used with the mfrs fan data chart,will easliy tell if the filter can be added safely.

The media filter ,although more sq ft,is more restrictive than the smaller furnace filter,if the furnace filter is just a standard filter.

return air

On a trane 4 ton drive system , The directions say to pull off the bottom for even flow thru the blower motor & wheel . Both sides would also work . Drawing air thru one side & running flex duct is the easy way but not always the right way . I try to run hard pipe & or over size the flex with the rightt size boots & hard pipe at the registers . Im not sure about your goodman but I would think return air doesnt know what brand of furnace's . bh

My avatar is a picture of a Goodman Silencer .....These were commonly used in Goodman country ....Photos by hvac tech ( PaysonHVAC )